From 52a593cdb14ed732b5580bbed39c0325815adedf Mon Sep 17 00:00:00 2001 From: Angus Gratton Date: Wed, 4 Sep 2024 17:17:38 +1000 Subject: [PATCH] py/scheduler: Only run callbacks on the main thread if GIL is disabled. Otherwise it's very difficult to reason about thread safety in a scheduler callback, as it can run at any time on any thread - including racing against any bytecode operation on any thread. This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton --- docs/library/micropython.rst | 8 ++++++++ py/scheduler.c | 8 +++++++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/docs/library/micropython.rst b/docs/library/micropython.rst index b17dfa9a75..31b24903f1 100644 --- a/docs/library/micropython.rst +++ b/docs/library/micropython.rst @@ -136,6 +136,14 @@ Functions the heap may be locked) and scheduling a function to call later will lift those restrictions. + On multi-threaded ports, the scheduled function's behaviour depends on + whether the Global Interpreter Lock (GIL) is enabled for the specific port: + + - If GIL is enabled, the function can preempt any thread and run in its + context. + - If GIL is disabled, the function will only preempt the main thread and run + in its context. + Note: If `schedule()` is called from a preempting IRQ, when memory allocation is not allowed and the callback to be passed to `schedule()` is a bound method, passing this directly will fail. This is because creating a diff --git a/py/scheduler.c b/py/scheduler.c index 3eae8b4fa3..2170b9577e 100644 --- a/py/scheduler.c +++ b/py/scheduler.c @@ -236,7 +236,13 @@ void mp_handle_pending(bool raise_exc) { // Handle any pending callbacks. #if MICROPY_ENABLE_SCHEDULER - if (MP_STATE_VM(sched_state) == MP_SCHED_PENDING) { + bool run_scheduler = (MP_STATE_VM(sched_state) == MP_SCHED_PENDING); + #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL + // Avoid races by running the scheduler on the main thread, only. + // (Not needed if GIL enabled, as GIL ensures thread safety here.) + run_scheduler = run_scheduler && mp_thread_is_main_thread(); + #endif + if (run_scheduler) { mp_sched_run_pending(); } #endif